Now I'm no genius like I am sure a lot of you are. I am just considering a fuel that may be easy to find, something that would be floating in a nebulae or even just inert in space. Is such a thing even possible? any suggestions/ theory/ insight would be appreciated.

There is a book by Ulrich Walter, the known german astronaut, in which he mentions that a Bussard ramjet would have to have a diameter of 7000 km to be able to collect hydrogen atoms in te interstellar space.

So nebulae might be more proper to apply Bussard collectors. May be Walter says something about it - I will have to have a look into his book. But as far as I know even in nebulae the gas still is very thin.

More interesting regions might be the radition belts of gas giants as well as the closer surroungings of stars.

What about experiments within the mercurian orbit or in the jovian radiation belt?

I am wondering, if gasses in a nebulae are sparse, how much more sparse would they be in open space?, which is in fact the question i was inquiring about, a gas that could be easily found and able to form a power source.

sorry i need to edit, i'm not considering gas only as a power source, radiation, particles, etc are what i'm considering, any open ideas on some way we could power our space vehicles without being supplied from earth are more what I'm thinking of.

well its a (comparatively) easy problem in statistical thermodynamics to calculate the temperature and pressure of the photon gas in the universe. i don't remember the result but you could look it up. as far as particles with mass go, i have no idea but my guess is there's something along the lines of no more than 1 hydrogen nucleus (maybe ionized maybe not) per m3, possibly less than that, in interstellar space. that being said there are probably more weird particles that are spontaneously generated and vanishing but that's above my head if so.